1. Field of the Invention
The present invention relates to an alignment device and method adapted to be used in various manufacturing or inspecting apparatus such as an exposure apparatus for use in the manufacturing process of semiconductor devices or liquid crystal display devices, or a coordinate measuring apparatus, and more particularly such alignment device provided with a focusing mechanism.
2. Related Background Art
In the manufacturing process of the semiconductor devices and the liquid crystal display devices, there has been employed an alignment device for precisely positioning a wafer, on which the semiconductor devices are formed, or a glass plate on which the liquid crystal display devices are formed, in a desired position by detecting an alignment mark (wafer mark) provided on such wafer or glass plate. In an example of semiconductor device manufacture to be explained in the following, the wafer has to be subjected to 10 to 20 superposed exposures on an exposure apparatus such as an aligner or a stepper, and it has been required to improve the precision of such superposed exposures. The alignment device is composed of an alignment sensor for detecting the positions of the wafer marks and a control system for determining the target position of the wafer, based on thus detected positions.
In such process, it is difficult to detect the positions of all the wafer marks with a single alignment sensor, because the surface coarseness varies depending on the exposures and the subsequent processes, and also because a step difference may exist between the wafer mark and the surrounding surface of the wafer, depending on the layer structure thereon. For this reason, following an alignment sensors are used, depending on the purpose:
1) LSA (laser step alignment) sensor: an alignment sensor system for irradiating the wafer mark with laser beam and measuring the position of the wafer mark by the diffracted or scattered light; utilized widely in various wafer processes; PA1 2) FIA (field image alignment) sensor: a sensor for position measurement by processing the image of a wafer mark, formed by illumination with light of a wide wavelength band obtained for example from a halogen lamp; effective for the measurement of an asymmetrical mark on an aluminum layer or on the wafer surface; and PA1 3) LIA (laser interferometric alignment) sensor: an alignment sensor system for irradiating a wafer mark formed as a diffraction grating with laser beams of slightly different frequencies from two directions and detecting the position of the wafer mark from the phase of the interference light obtained by interference of two diffracted lights generated from said wafer mark; effective for a wafer mark of a small step difference or for a wafer with significant surface coarseness. PA1 an objective optical system for detecting the light from a 1st alignment mark formed in a 1st mark area on a substrate and the light from a 2nd alignment mark formed in a 2nd mark area; PA1 a 1st detection optical system having a 1st detection area in the viewing field of said objective optical system and adapted to detect the light from said 1st mark through said objective optical system; PA1 a 2nd detection optical system having a 2nd detection area, different from said 1st detection area, in the viewing field of said objective optical system and adapted to detect the light from said 2nd mark through said objective optical system; and PA1 a focus detection system for irradiating said 1st and 2nd detection areas respectively with light beams and respectively receiving reflected lights, thereby detecting the deviation of said 1st mark area with respect to the focal plane of said 1st detection optical system and the deviation of said 2nd mark area with respect to the focal plane of said 2nd detection optical system.
These alignment sensors have been selectively utilized depending on the applications.
The optical systems are generally provided with auto focusing mechanisms, and the alignment sensor is also provided with an auto focusing mechanism for maintaining the inspected surface within a predetermined range with respect to the alignment sensor (such function being also called focusing). Such auto focusing mechanism is composed of an auto focusing sensor for irradiating the object wafer mark with detecting light beam and detecting the axial (focus) position of the inspected surface from the reflected light, and a drive mechanism for setting said focus position at a predetermined (in-focus) position. However, even if alignment sensors of plural kinds are provided, there is provided only one auto focusing sensor, for irradiating the predetermined measuring point on the wafer with a light beam for focus position measurement, for common use by these alignment sensors.
Because of the recent increase of the sensors of various kinds incorporated in the exposure apparatus, an efficient arrangement is desired for the accessory devices of the exposure apparatus. For this reason, there has been recently employed an alignment system which incorporates, as disclosed in the Japanese Patent Application Laid-Open No. 5-291109, plural different alignment sensors in a common objective lens.
In such alignment system with plural alignment sensors utilizing a common objective lens, the range of height of the inspected surface (focusing range), in which the position detection can be achieved most precisely, differs slightly among the plural alignment sensors. Consequently, when the wafer surface is set at a height by irradiating a predetermined portion of the wafer with a focus position detecting light beam and utilizing the reflected light in the conventional manner, the optimum surface height for a certain alignment sensor may not be optimum for another alignment sensor, so that some alignment sensors may become incapable of exact position detection.